As for a mounting table for mounting thereon an object to be processed (wafer) and a focus ring, there is disclosed a mounting table including a base portion having a coolant path formed therein and an electrostatic chuck for electrostatically attracting the object to be processed, the electrostatic chuck being provided on the base portion and having a contact surface that contacts with a backside of the object to be processed (see, e.g., Japanese Patent Application Publication No. 2011-9351). In the mounting table disclosed in Japanese Patent Application Publication No. 2011-9351, the base portion has a first top surface on which the electrostatic chuck is disposed, a ring-shaped second top surface which is disposed at a position lower than the first top surface and outer than the first top surface and on which the focus ring is provided, and a side surface extending in a vertical direction between the first top surface and the second top surface. In this mounting table, a first path disposed below the first top surface and a second path disposed below the second top surface are provided as a coolant path.
Further, gas grooves for uniformly distributing a heat transfer gas to the backside of the object to be processed are provided on the top surface of the electrostatic chuck which contacts with the backside of the object to be processed. Due to the presence of the gas grooves, protrusions are formed on the top surface of the electrostatic chuck.
However, in the mounting table disclosed in Japanese Patent Application Publication No. 2011-9351, heat from the focus ring is transferred to the mounting table (e.g., an inner side surface of the mounting table) via a member provided above the second path, and this may affect a temperature of an edge region of the object to be processed. Therefore, the temperature distribution becomes non-uniform between the central region and the edge region of the object to be processed. As a result, the quality of the object to be processed may deteriorate.